The purpose of this research is to identify the factors that control the transition of a replicative population of skin basal cells into non-replicative population of malpighian cells. During this transition, marked changes in the cell surface of basal cells takes place, and this proposal will focus at the molecular level on how glycoproteins of the surface membrane affect this transition. Using trypsin-release techinques to isolate skin epithilial cells and collagen gels to cultivate cells, two populations of keratinocytes will be isolated and studied: a replicative and a non-replicative one. Methods to isolate surface membranes from each of the populations will be developed, and a chemical analysis will be made of their major protein and carbohydrate constituents. The synthesis, degradation, and turnover of fucosylated proteins will be determined in replicative and non-replicative cell, and a peripheral surface glycoprotein will be isolated from non-replicative cells and characterized. The ability of surface glycoproteins from non-replicative cells to interact with and to attach to the surface of replicative cells will be studies, and the effect of these proteins on the transition from a replicative form to a non-replicative form will be analyzed. The binding of 121I-EGF will be determined during the transition. The changes in the cell surface of basal cells stimulated to divide in vivo by cellophane tape stripping will be studied, and the ability of a purified glycoprotein to inhibit a GO to S transition when either topically applied or systemically administered to experimental animals will be determined.